The invention relates to a filter module with a number A of circular filter cells, a number Axe2x88x921 of spacer rings and with two end rings, the filter cells and the rings being combined in a stack with the formation of a central through channel by means of clamping elements which are spaced apart in the peripheral direction of the channel wall and which engage the end rings on the inside to transfer axial clamping forces.
In these filter modules the filter cells ordinarily consist of two circular sections of a filter material which are held together on the outer periphery and between which otherwise discharge channels for the filtrate are formed by means of spacer elements.
In conventional filter modules a central support tube with radial passages is often used to be able to combine the filter cells into a stack (compare DE-OS 37 41 552 A1, DE-OS 40 26 934 A1). This construction is relatively complex and therefore has been replaced by a construction of the initially mentioned type in which the support tube can be abandoned.
In these filter modules the clamp elements consist of sheet metal bands which are angled on the end side and which in the peripheral direction are located spaced apart within the through channel and are supported with their ends angled to the outside on the end rings of the stack. The elastic restoration forces of the filter material provide for the clamp elements to be held under prestress and for their being unable to unintentionally move radially to the inside and therefore always remaining engaged with the end rings. When the filter module is installed in the filter housing, it is however compressed axially via suitable clamping means so far that the clamp elements are no longer under prestress and therefore can be easily released from their holding position. This results in that the filter module is no longer held together when it is replaced and falls apart into its individual parts. This is undesirable because dismantling becomes difficult and the disposal of used filter modules is time-consuming.
Another disadvantage of the known filter modules is that the clamp elements which consist of steel make it difficult to reprocess the other components of the filter module which are usually plastic. The clamp elements must be sorted out before the other material can be processed xe2x80x9csortedxe2x80x9d and re-used.
Thus, in a filter module of the initially mentioned type in which a central support tube is no longer necessary, the object is to overcome the indicated disadvantages of the known clamp elements and to propose a filter module in which the clamp elements reliably hold the stack of filter cells together even after the external clamping forces have been relieved. Moreover, it should be possible to produce the clamp elements out of a material which together with the other parts of the filter module can be reused or disposed of as easily as possible.
To achieve this object it is proposed as claimed in the invention that the clamp elements consist of bands with ends which are made hook-shaped and which can be fixed on the end rings by means of an essentially radial hooking or locking motion and that there are means which prevent unintentional radial unhooking or unlocking motion of the hook-shaped ends.
In the production of the filter modules as claimed in the invention the clamp elements, like the known steel clamp elements, are spaced in the peripheral direction of the channel lip wall and are hooked or locked into the end rings. The elastic restoration forces of the filter material here also provide for the clamp elements to be under axial prestress for installation of the filter module in the filter housing. In the illustrated cancellation of this prestress by external clamping forces when the filter module is installed in the filter housing the bands as claimed in the invention are likewise relieved, but due to the provided retaining means cannot radially unhook or unlock, so that the stack of filter cells is held together by the clamp elements consisting of the bands even when it has been removed from the filter housing. The filter module can therefore not fall apart into its individual parts and is much easier to handle in disposal and reprocessing than the host of its individual parts.